<template>
    <div class="slider" ref="slider">
      <div class="slider-group" ref="sliderGroup">
        <slot></slot>
      </div>
      <div class="dots">
        <span class="dot" v-for="(item,index) in dots" :class="{active:currentPageIndex===index}" :key="item"></span>
      </div>
    </div>
</template>

<script>
import {addClass} from 'common/js/dom'
import BScroll from 'better-scroll'

export default {
  name: 'slider',
  props: {
    loop: {
      type: Boolean,
      default: true
    },
    autoPlay: {
      type: Boolean,
      default: true
    },
    interval: {
      type: Number,
      default: 3500
    }
  },
  data () {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  mounted () {
    // 由于数据是异步加载的，所以除了加延迟外，还需要在外部添加v-if确保数据加载完毕再渲染组件
    setTimeout(() => {
      this._setSliderWidth()
      this._initDots()
      this._initSlider()
      if (this.autoPlay) {
        this._play()
      }
    }, 20)

    // 窗口resize
    window.addEventListener('resize', () => {
      if (!this.slider) {
        return null
      }
      this._setSliderWidth(true)
      this.slider.refresh()
    })
  },
  methods: {
    // 计算滑动内容的宽度
    _setSliderWidth (isResize) {
      this.children = this.$refs.sliderGroup.children
      let width = 0
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0, len = this.children.length; i < len; i++) {
        let child = this.children[i]
        addClass(child, 'slider-item')
        child.style.width = sliderWidth + 'px'
        width += sliderWidth
      }
      // 窗口调整大小时，无需再增加2个sliderWidth
      if (this.loop && !isResize) {
        width += 2 * sliderWidth
      }
      this.$refs.sliderGroup.style.width = width + 'px'
    },
    // 初始化slider
    _initSlider () {
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        momentum: false,
        snap: {
          loop: this.loop,
          threshold: 0.3
        }
      })
      // scrollEnd事件，获取当前滚动的页码
      this.slider.on('scrollEnd', () => {
        let pageIndex = this.slider.getCurrentPage().pageX
        this.currentPageIndex = pageIndex
        if (this.autoPlay) {
          clearTimeout(this.timer)
          this._play()
        }
      })
    },
    // 初始化dots
    _initDots () {
      this.dots = new Array(this.children.length)
    },
    // 轮播到下一张
    _play () {
      this.timer = setTimeout(() => {
        this.slider.next(400)
      }, this.interval)
    }
  },
  destroyed () {
    clearTimeout(this.timer)
  }
}
</script>

<style lang="less" scoped>
@import "~common/css/variable";
.slider {
  min-height: 1px;
  .slider-group {
    position: relative;
    overflow: hidden;
    white-space: nowrap;
    .slider-item {
      float: left;
      box-sizing: border-box;
      overflow: hidden;
      text-align: center;
      a{
        display: block;
        width: 100%;
        overflow: hidden;
        text-decoration: none;
      }
      img {
        display: block;
        width: 100%;
      }
    }
  }
  .dots {
    position: absolute;
    right: 0;
    left: 0;
    bottom: 12px;
    text-align: center;
    font-size: 0;
    .dot{
      display: inline-block;
      margin: 0 4px;
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: @color-text-l;
      &.active {
        width: 20px;
        border-radius: 5px;
        background: @color-text-ll;
      }
    }
  }
}
</style>
